Solid State Tissue Equivalent Detector With Gate Electrodes

ABSTRACT

An organic semiconductor detector for detecting radiation has an organic conducting active region, an output electrode and a field effect semiconductor device. The field effect semiconductor device has a biasing voltage electrode and a gate electrode. The organic conducting active region is connected on one side to the field effect semiconductor device and is connected on another side to the output electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to provisional U.S. patentapplication Ser. No. 62/570,735, filed Oct. 11, 2017, and entitled“Solid Stste Tissue Equivalent Radiation Detector Improvement,” thedisclosure of which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTINGCOMPACT DISC APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

This invention concerns a novel type of a Solid State Tissue EquivalentDetectors (SSTEDs) that combines semiconductor device constructionprinciples and organic photo-conductor technology. The detector is animprovement on the invention disclosed in U.S. Pat. No. 8,350,225, whichis hereby incorporated by reference in its entirety, issued to the sameinventor. The invention is a solid state device that has an activeregion made of organic material; the entire device (with the exceptionof the electrical contacts) can be composed of organic material; it issmall and lightweight; will operate at a relatively low voltage; and,will have a tissue equivalent response based on its constituent organiccomponents.

The device is an improvement on the device presented in U.S. Pat. No.8,350,225 with a modification introducing new electrodes. The newelectrodes effectively make regions of the device, which are connectedto the active region, act like Field Effect Transistors (FETs). The newelectrodes act like gate regions of a standard FET and create fieldeffect within regions of the device. Field effect refers to themodulation of the electrical conductivity of a material by theapplication of an external electric field. Thus, when the device is at aresting voltage and the FETs' resistance is very high, the active regionis insulated preventing charge within the active region from draining.The new gate electrodes allow charges to be cleared from the activeregion when positive or negative voltage is applied to the gates therebyreducing the resistance of the FETs.

BRIEF SUMMARY OF THE INVENTION

An embodiment of the present invention is an organic semiconductordetector for detecting radiation comprising an organic conducting activeregion, an output electrode and a field effect semiconductor device. Thefield effect semiconductor device comprises a biasing voltage electrodeand a gate electrode. The organic conducting active region is connectedon one side to the field effect semiconductor device and is connected onanother side to the output electrode.

In another embodiment of the present invention, the field effectsemiconductor device further comprises a channel region and aninsulation region. The biasing voltage electrode is connected to thechannel region. The insulation region electrically insulates the gateelectrode and the channel region.

In yet another embodiment of the present invention, the channel regionis a Pentacene channel region and the insulation region is a Paryleneinsulation region.

In another embodiment of the present invention, the organic conductingactive region, the output electrode, the gate electrode and the biasingvoltage electrode are made of PEDOT layers deposited on a PEN substrate.

In yet another embodiment of the present invention, a voltage at theoutput electrode is held at a constant level when the organicsemiconductor detector is not being irradiated.

In another embodiment of the present invention, the constant level is 2volts.

In yet another embodiment of the present invention, the organicconducting active region becomes positively electrically charged whenthe organic semiconductor detector is being irradiated with ionizingradiation. The voltage at the output electrode increases above theconstant level when the organic conducting active region becomespositively electrically charged.

In another embodiment of the present invention, a negative voltageapplied to the gate electrode when the organic conducting active regionbecomes positively electrically charged drains the positive electricalcharge of the organic conducting active region and returns the voltageat the output electrode to the constant level.

In yet another embodiment of the present invention, the organicsemiconductor detector for detecting radiation is configured as adosimeter. The organic conducting active region becomes positivelyelectrically charged when the organic semiconductor device is beingirradiated with ionizing radiation. A gate voltage is applied to thegate electrode while the organic semiconductor detector is beingirradiated. The gate voltage is determined so as to maintain the voltageat the output electrode at the constant level when the organicsemiconductor detector is being irradiated. The gate voltage isrepresentative of a dose of ionizing radiation received by the organicconducting active region.

In another embodiment of the present invention, an organic semiconductordetector for detecting radiation comprises an organic conducting activeregion, an output electrode, a first field effect semiconductor deviceand a second field effect semiconductor device. The first field effectsemiconductor device comprises a first biasing voltage electrode and afirst gate electrode. The second field effect semiconductor devicecomprises a second biasing voltage electrode and a second gateelectrode. The organic conducting active region is connected to thefirst field effect semiconductor device and to the second field effectsemiconductor device. The organic conducting active region is connectedto the output electrode.

In yet another embodiment of the present invention, the first fieldeffect semiconductor device further comprises a first channel region anda first insulation region and the second field effect semiconductordevice further comprises a second channel region and a second insulationregion. The first bias voltage electrode is connected to the firstchannel region and the second bias voltage electrode is connected to thesecond channel region. The first insulation region electricallyinsulates the first gate electrode and the first channel region and thesecond insulation region electrically insulates the second gateelectrode and the second channel region.

In another embodiment of the present invention, the first channel regionand the second channel region are Pentacene channel regions and thefirst insulation region and the second insulation region are Paryleneinsulation regions.

In yet another embodiment of the present invention, the organicconducting active region, the output electrode, the first gateelectrode, the second gate electrode, and the first biasing voltageelectrode, and the second biasing voltage electrode are made of PEDOTlayers deposited on a PEN substrate.

In another embodiment of the present invention, a voltage at the outputelectrode is held at a constant level when the organic semiconductordetector is not being irradiated.

In yet another embodiment of the present invention, a negative voltageapplied to the first gate electrode drains a positive electrical chargeof the organic conducting active region when the organic conductingactive region becomes positively electrically charged and returns thevoltage at the output electrode to the constant level. A positivevoltage applied to the second gate electrode drains a negativeelectrical charge of the organic conducting active region when theorganic conducting active region becomes negatively electrically chargedand returns the voltage at the output electrode to the constant level.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The advantages and features of the present invention will be betterunderstood as the following description is read in conjunction with theaccompanying drawings, wherein:

FIG. 1 is an illustration of an embodiment for the Solid State TissueEquivalent Detector (SSTED).

FIG. 2 is an illustration of a cross-section of an embodiment of thepresent invention.

FIG. 3 is a graphical illustration of the response of an embodiment ofthe present invention to microbeam radiation.

For clarity purposes, all reference numerals may not be included inevery figure.

DETAILED DESCRIPTION OF THE INVENTION

SSTEDs pursuant to the present invention are capable of measuringionizing radiation using organic semiconductors. The devices arepreferably fabricated on PEN (Polyethylene Naphthalate) substrates usingthe process described below. It is important to recognize that a largeportion of the device which is exposed to radiation is constructed fromorganic material. This is a key feature, enabling the device to functionas a tissue equivalent radiation detector. A material's radiation crosssection is generally dependent on: (1) the atomic number of itsconstituent components, (2) the overall density of the material, and (3)the energy, character, characteristics, and/or quality of the incidentionizing radiation.

The atomic number of the constituent components of the materials used inthe device is dictated by the chemical makeup of the material. Thedevices preferably are constructed from organic compounds to ensure thatthe atomic numbers and the relative proportions primarily match those oforganic tissue. The atomic numbers of the constituent components for thedevice are selected so that the density of the active region isapproximately the same density as the density of normal human tissue.The devices are primarily built from the same constituent components(e.g., Oxygen, Carbon, Hydrogen) as organic tissue with roughly the samedensity as material within a human cell. Consequently, from an ionizingradiation perspective, these devices have very similar radiation crosssection as tissue, independent of the radiation energy and quality.

The SSTEDs pursuant to this invention respond appropriately to ionizingradiation of different qualities and energy. FIG. 1 shows a diagram ofthe structure of an embodiment of the SSTED. As illustrated in FIG. 1,the device 10 comprises two field effect semiconductor device regions 12and 13 (for clarity referred to as FETs), each having a drain biasvoltage electrode (“drain”) (identified with V−) and a source biasvoltage electrode (“source”) (V+) and a gate electrode 111 or 112. Thedrain (V−) of FET 12 and the source (V+) of FET 13 are connected to anorganic conducting active region (“Active Region”) 310. The Gate 111 ofFET 12 is connected via a gate connector 101 to an electrical contact101 a. The Gate 112 of FET 13 is connected via a gate connector 102 toan electrical contact 102 a. The source (V+) of FET 12 is connected viaa connector 301 to electrical contact 301 a, and the drain (V−) of FET13 is connected via a connector 302 to electrical contact 302 a.

While FIG. 1 illustrates an embodiment with two field effect regions,the device can operate with a single field effect device region, forexample FET 13. Adding a second field effect device region, e.g., FET12, facilities in balancing the system, but is not required foroperation, as will be understood by a person skilled in the art.

Also as illustrated on FIG. 1, the Active Region 310 is connected via aconnector 305 to an electrical contact 305 a. The electrical connector305 a is further connected to additional circuitry 20 comprising anOp-Amp with an output 21.

FIG. 2 illustrates a cross section of FET 12. A cross section of FET 13is the same and is not shown. FET 12 is formed on the substrate 11 bydepositing layers of different materials, as described in more detailbelow. The FET 12 comprises a gate 111, insulation 201, channel 401,source 302 electrode, and drain 301 electrode. Insulation 201 insulatesthe gate electrode 111 and the gate connector 101 of the FET 12 from therest of the FET structure so that the application of a gate voltage tothe gate connector 101 (or electrical contact 101 a) does not causecurrent to run within the rest of the FET structure, thereby creatingthe “field effect” in the FET structure.

The device 10 may be manufactured by printing or depositing layers ofdifferent materials on a substrate 11, preferably made of PEN. In thisembodiment the first layer deposited on the substrate 11 is composed ofa conducting polymer, preferably PEDOT(Poly(3,4-ethylenedioxythiophene)) and forms the gate electrodes 111,112, the gate connectors, 101, 102, and electrical contacts 101 a, 102a. The second layer is composed of a non-conducting polymer, preferablyParylene, and is deposited only in the region of the gate electrodes111, 112 of the FET 12, 13. The second layer forms the insulation 201(FIG. 2). The third layer deposited on the substrate is composed of aconducting polymer, preferably PEDOT. The third layer forms the ActiveRegion 310, the output connection 305 and connector 305 a. The thirdlayer also forms the source 301, 303 and drain 302, 304 connectors ofFETs 12, 13, and the electrical connectors 301 a, 302 a. The fourthlayer is composed of high mobility organic semiconductor, preferablyTIPS pentacene (6,13-Bis(triisopropylsilylethynyl) and forms the channelregions 401 of the FETs 12, 13. TIPS pentacene is a relatively highmobility organic semiconductor that is well suited for FET construction.It is also a reasonably good photoconductor, and this is exploited whenthe SSTEDs undergo testing of the devices structural integrity.

Within the device 10 a large portion of the third layer serves as theActive Region 310. The Active Region 310 has substantially larger volume(e.g., 50-200, or more, times larger) than any other feature orcomponent within the device 10. This substantially larger volume can beachieved by increasing the area and/or thickness of the material formingActive region 310. The Active Region 310 becomes charged when the deviceis irradiated with ionizing radiation. The embodiment of device 10illustrated in FIG. 1 includes a biasing amplifier 20. FETs 12, 13 areextremely high resistance when a positive or ground voltage is appliedto the gate electrodes 111, 112, for example via the gate connectors,101, 102, and contacts 101 a, 102 a.

Under these bias voltage conditions FETs 12, 13 act as resistors withresistances in the Giga Ohm (GΩ) range. The FETs 12, 13 therefore form avoltage divider and the voltage (Vout) at contact 305 a measured betweenthe points 303 and 304 where the FET pair is connected to the ActiveRegion 310 can be held at a constant voltage at rest (e.g., when thedevice is not irradiated) (“resting voltage”). Assuming the device 10comprises two FETs, and the FETs have equal resistances, the restingvoltage can be approximately (V+−V−)/2. The voltages V+ and V− can alsobe adjusted so that at rest the Active Region 310 is held at differentresting voltage, as measured at Vout at contact 305 a. The value for theresting voltage is chosen to lie within the operating characteristics ofthe operational amplifier 20 used for the device 10, while taking intoconsideration the overall noise in the system, and the characteristicsof the other components in the system. For example, if the max voltageof op-amp 20 is 4.5V, the resting voltage can be between 0V and 4.5V,but preferably will be closer to the middle of this range, around 2V.With other types of amplifiers the resting voltage can have differentvalues.

The operational amplifier (“op-amp”) 20 preferably is a femto-ampereinput bias precision amplifier and is chosen so that it can sense smallcharge accumulations in the Active Region 310 without affecting themeasurement. Such op-amps are typically used for electrometermeasurements like the ones being described herein. For example, TexasInstruments LMP7721MA, or similar op-amps can be used. The op-amp 20 isconfigured as a voltage follower, isolating the Active Region 310 fromdownstream electronics. This isolation is required because the chargebuildup in the Active Region 310 due to irradiation is small and anycharge from other electronics leaking to the Active Region 310 willadversely affect the measurement. In the initial or un-exposed state theActive Region 310 is nominally held at the resting voltage (as describedabove). The voltage follower configuration of op-amp 20 does not provideany gain, and as a result the voltage at contact 21 will nominally bethe same as the voltage at contact 305 a, in both contacts representedby Vout in FIG. 1. Because FETs 12, 13 are extremely high resistance(e.g., in the GΩ range) effectively insulating the Active Region 310,the Active Region 310 essentially is held at the resting voltage but is“free standing.” By “free standing” it is meant that the Active Region310 is primarily connected to the op-amp 20 and isolated from everythingelse.

When the device 10 is irradiated with ionizing radiation the ActiveRegion 310 becomes ionized as electrons are driven out of the ActiveRegion 310. The Active Region 310 thus becomes more positively chargedand the value of Vout at connector 305, and at connector 21 willincrease above the resting voltage. Because the input impedance of theop-amp 20 and the resistance of the FETs 12, 13 are very high, there isvery insignificant conduction path to bring the voltage in the ActiveRegion 310 back to the resting voltage. The insignificant conductionthrough the FET 12, 13 will drain the charge of the Active Region 310(or equalize the charge) over a long period of time. To speed up thedraining of the charge from the Active Region 310 a negative voltage canbe applied to the gate electrode 112 of FET 13. Applying negativevoltage to gate connector 102, which is connected to gate electrode 112,will reduce the resistance of FET 13 and allow conduction through FET 13to drain the positive charge from the Active Region 310 and restore theActive Region 310 to the resting voltage.

In a situation when the Active Region 310 is negatively charged, it canbe returned to resting voltage by applying positive voltage to gateelectrode 111 of FET 12. While the device 10 is at rest positive voltagemay also be applied to gate electrodes 111 and 112 to increase thecharge and increase the resistance of FETs 12, 13. Control of the gateis managed by a separate control board that in this embodiment isArduino based, but maybe any other suitable electronics control boardknown in the art.

FIG. 3 shows a test response of an SSTED embodiment of this invention toa 300 μm wide beam of 40 kV X-rays irradiating the center of the ActiveRegion 310. For the test the beam was produced by X-ray Diffraction(XRD) crystallography apparatus. The X-ray tube voltage and current canbe adjusted, and the exposure time is always 5 seconds in the figure.The “0” value of the Y axis represents resting voltage, and the Y-axisshows volts above the resting voltage measured at Vout, and the X-axisshows time in minutes and seconds. Each peak on the graph of FIG. 3coincides with X-Ray exposure of the Active Region 310 of device 10.FIG. 3 shows nine peaks corresponding to nine periods of X-Ray exposureof the Active Region 310. As FIG. 3 illustrates, at each peak differentmaximum voltages above resting voltage were registered, corresponding todifferent intensities of X-Ray radiation.

The tail after each peak on FIG. 3 indicates the time it takes to bringthe Active Region 310 back to resting voltage by applying voltage to thegate electrode 112 of FET 13. In this experiment a small bias voltagewas applied to gate electrode 112 via gate connector 102 and contact 102a. A different implementation of a biasing mechanism would be to holdthe output voltage Vout constant by applying a feedback voltage fromoutput connector 21 or 305 a to gate connector 102 and varying thevoltage applied at gate connector 102 depending on the value of thefeedback voltage. The voltage thus applied at gate electrode 112 (e.g.,via gate connector 102, contact 102 a) to maintain a constant Vout wouldbe representative of the intensity of the ionizing radiation and can beused as an effective dosimeter output. The SSTEDs have been probed withthe 300 μm microbeam across the entire surface of the device. This is anextremely important measurement if the device is to be truly tissueequivalent. When materials are exposed to ionizing radiation, theynaturally become charged. It is necessary for us to only measure thecontribution from organic regions of the device. The contributions fromother regions of the device are found to negligible, proving that theresponse to ionizing radiation will mainly arise from charge generationwithin the Active Region 310.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes, omissions, and/or additions may be made and equivalentsmay be substituted for elements thereof without departing from thespirit and scope of the invention. In addition, many modifications maybe made to adapt a particular situation or material to the teachings ofthe invention without departing from the scope thereof. Therefore, it isintended that the invention not be limited to the particular embodimentsdisclosed as the best mode contemplated for carrying out this invention,but that the invention will include all embodiments falling within thescope of the appended claims. Moreover, unless specifically stated anyuse of the terms first, second, etc. do not denote any order orimportance, but rather the terms first, second, etc. are used todistinguish one element from another.

I claim:
 1. An organic semiconductor detector for detecting radiationcomprising: an organic conducting active region; an output electrode;and a field effect semiconductor device comprising a biasing voltageelectrode and a gate electrode; wherein the organic conducting activeregion is connected on one side to the field effect semiconductordevice; and, wherein the organic conducting active region is connectedon another side to the output electrode.
 2. The organic semiconductordetector for detecting radiation of claim 1, wherein the field effectsemiconductor device further comprises a channel region and aninsulation region; wherein the biasing voltage electrode is connected tothe channel region; and, wherein the insulation region electricallyinsulates the gate electrode and the channel region.
 3. The organicsemiconductor detector for detecting radiation of claim 2, wherein thechannel region is a Pentacene channel region; and, wherein theinsulation region is a Parylene insulation region.
 4. The organicsemiconductor detector for detecting radiation of claim 1, wherein theorganic conducting active region, the output electrode, the gateelectrode and the biasing voltage electrode are made of PEDOT layersdeposited on a PEN substrate.
 5. The organic semiconductor detector fordetecting radiation of claim 1, wherein a voltage at the outputelectrode is held at a constant level when the organic semiconductordetector is not being irradiated.
 6. The organic semiconductor detectorfor detecting radiation of claim 5, wherein the constant level is 2volts.
 7. The organic semiconductor detector for detecting radiation ofclaim 5, wherein the organic conducting active region becomes positivelyelectrically charged when the organic semiconductor detector is beingirradiated with ionizing radiation; and, wherein the voltage at theoutput electrode increases above the constant level when the organicconducting active region becomes positively electrically charged.
 8. Theorganic semiconductor detector for detecting radiation of claim 7,wherein a negative voltage applied to the gate electrode when theorganic conducting active region becomes positively electrically chargeddrains the positive electrical charge of the organic conducting activeregion and returns the voltage at the output electrode to the constantlevel.
 9. The organic semiconductor detector for detecting radiation ofclaim 5, wherein the organic semiconductor detector is configured as adosimeter, wherein the organic conducting active region becomespositively electrically charged when the organic semiconductor device isbeing irradiated with ionizing radiation; wherein a gate voltage isapplied to the gate electrode while the organic semiconductor detectoris being irradiated; wherein the gate voltage is determined so as tomaintain the voltage at the output electrode at the constant level whenthe organic semiconductor detector is being irradiated; and, wherein thegate voltage is representative of a dose of ionizing radiation receivedby the organic conducting active region.
 10. An organic semiconductordetector for detecting radiation comprising: an organic conductingactive region; an output electrode; a first field effect semiconductordevice comprising a first biasing voltage electrode and a first gateelectrode; and, a second field effect semiconductor device comprising asecond biasing voltage electrode and a second gate electrode; whereinthe organic conducting active region is connected to the first fieldeffect semiconductor device and to the second field effect semiconductordevice; and, wherein the organic conducting active region is connectedto the output electrode.
 11. The organic semiconductor detector fordetecting radiation of claim 10, wherein the first field effectsemiconductor device further comprises a first channel region and afirst insulation region and the second field effect semiconductor devicefurther comprises a second channel region and a second insulationregion; wherein the first bias voltage electrode is connected to thefirst channel region and the second bias voltage electrode is connectedto the second channel region; and, wherein the first insulation regionelectrically insulates the first gate electrode and the first channelregion and the second insulation region electrically insulates thesecond gate electrode and the second channel region.
 12. The organicsemiconductor detector for detecting radiation of claim 11, wherein thefirst channel region and the second channel region are Pentacene channelregions and the first insulation region and the second insulation regionare Parylene insulation regions.
 13. The organic semiconductor detectorfor detecting radiation of claim 10, wherein the organic conductingactive region, the output electrode, the first gate electrode, thesecond gate electrode, the first biasing voltage electrode, and thesecond biasing voltage electrode are made of PEDOT layers deposited on aPEN substrate.
 14. The organic semiconductor detector for detectingradiation of claim 10, wherein a voltage at the output electrode is heldat a constant level when the organic semiconductor detector is not beingirradiated.
 15. The organic semiconductor detector for detectingradiation of claim 14, wherein a negative voltage applied to the firstgate electrode drains a positive electrical charge of the organicconducting active region when the organic conducting active regionbecomes positively electrically charged and returns the voltage at theoutput electrode to the constant level; and, wherein a positive voltageapplied to the second gate electrode drains a negative electrical chargeof the organic conducting active region when the organic conductingactive region becomes negatively electrically charged and returns thevoltage at the output electrode to the constant level.